This invention relates generally to modular flat panel display devices and particularly to a system for compensating for color impurities caused by horizontal beam landing errors in such devices.
A modular flat panel display device in which the instant invention can be utilized is described in U.S. Pat. No. 4,117,368 issued to F. J. Marlowe, et al. The Marlowe et al. device consists of an evacuated envelope which is divided into channels by a plurality of vanes. Each of the channels include guide meshes for propagating electron beams along the lengths of the channels. When a particular line of the visual display is to be produced, the electron beams are ejected from the guide meshes and travel toward the display screen. The vanes support deflection electrodes which are biased with varying deflection potentials. These deflection potentials cause the electrons traveling from the guide meshes to the display screen to be scanned transversely across the channels. The electron beams of all the channels are simultaneously ejected from between the guide meshes so that a portion of the same horizontal line of the visual display is simultaneously generated transversely across each of the channels.
U.S. Pat. No. 4,131,823 issued to T. L. Credelle shows a system for converging the electron beams in a flat panel display device of the type described in the Marlowe et al. patent. In the Credelle device, deflection electrodes of the type disclosed in the Marlowe et al. patent, are arranged on both sides of the internal support walls and extend the longitudinal dimension of the channels. Arranged on both sides of the deflection electrodes are guard, or convergence, electrodes which also extend along the longitudinal dimension of the channels. Accordingly, electron beams which are traveling from the beam propagation meshes toward the phosphor screen sequentially pass the first convergence electrode, the deflection electrode, and the second convergence electrode. The convergence electrodes are voltage biased to cause the electron beams to converge at the shadow mask which is arranged parallel to and spaced from the phosphor screen. The shadow mask contains apertures through which the electron beams must pass in order to strike the phosphor screen. Because the three electron beams pass through the apertures at different angles, each of the three beams strikes a different one of the phosphors so that different colors of light are emitted. The shadow mask therefore serves as a color selection electrode. The convergence potentials on the convergence electrodes cause all the electron beams to converge at the same point on the shadow mask and the deflection potentials on the deflection electrodes cause the convergence point of the three beams to transversely scan across the channels. Accordingly, the combined effect of the deflection potentials and the convergence potentials is that of causing the electron beams to converge at points along traverse lines across the shadow mask. The three beams pass through the shadow mask apertures at different angles whereby each electron beam strikes a different color phosphor and a color display is produced. Typically, in flat panel display devices the transverse and longitudinal dimensions are referred to as the horizontal and vertical dimensions respectively. These designations are adopted hereinafter.
The Marlowe and Credelle devices operate in the manner intended; however, minor structural variations in the display device can cause the electron beams to land at horizontal positions which are different from those intended. Because the electron beams are horizontally displaced, the beams pass through the shadow mask apertures at improper angles and the beams strike a phosphor of a color different from that intended. The instant invention overcomes this disadvantage by the provision of a system for providing voltages which compensate for horizontal beam landing errors to thereby substantially reduce or eliminate the color impurities which result from such landing errors.